The Ethernet PON (EPON) uses 1 gigabit per second (Gpbs) Ethernet transport, and the Gigabit PON (GPON) uses up to 2.5 Gbps of Ethernet transport. Both are suitable for very high-speed data applications, as well as for converged system support (telephone, video, etc.). The unprecedented amount of bandwidth in both is directed toward, and arriving from a single entity, the Optical Network Unit (ONU).
An Optical Line Terminal (OLT) manages remotely the transmission of each ONU. The OLT and the ONUs exchange messages. In each cycle of such an exchange, the OLT grants a grant to each ONU, which is answered by a report message from the ONU. The concept of “cycle” as used herein is explained in detail in PCT application PCT IL03/00702 by Onn Haran et al., filed 26 Aug. 2003, and titled “Methods for dynamic bandwidth allocation and queue management in Ethernet Passive Optical Networks”, which is incorporated herein by reference. The ONU has a queue manager that prepares queue status information, which is transmitted using Multipoint Control Protocol (MPCP) messages to the OLT to enable smart management. In other words, the ONU “informs its internal queues status” to the OLT. The OLT management is executed using a DBA algorithm. An efficient DBA algorithm is essential to guarantee Quality of Service (QoS), required to fulfill a Service Level Agreement (SLA). A SLA typically includes, among other things, a guaranteed BW, which is the BW that is allocated to an ONU whenever the ONU asks for it, regardless of the network load. Operator revenues are expected to increase from selling sophisticated SLAs to customers. High bandwidth utilization allows adding more customers to the network. Thus, an efficient DBA algorithm is an enabler to operator revenues.
Fragmentation loss is the amount of wasted grant time that is not utilized for packet transmission. The subject is also explained in detail in PCT application PCT IL03/00702. The reason for fragmentation is a lack of synchronization between the ONU queue status and the OLT knowledge of queue status. When this happens, the fragmentation can result in empty grant transmission, when the pending packets are larger than the given grant. This effect increases the transmission delay.
The basic existing schemes for reporting and granting cause fragmentation loss by damaging the synchronization between the OLT and an ONU. FIG. 1 presents such a reporting and granting scheme and the resulting damage to the synchronization. All k ONUs (ONU1 . . . ONUk) transmit their data and report their updated queue occupancy in step 100 (cycle n−1). The DBA in the OLT processes the reports in step 106 (cycle n) and determines the grants for transmissions occurring in step 104 (cycle n+1). While the DBA process the reports in step 106, the ONUs send more updated reports in step 102 (cycle n). The synchronization loss is caused because in step 104 the ONU already transmits some of the data that was reported in step 102, although the OLT meant to grant this data for step 104.
Other solutions require processing the reports one by one (“greedy algorithms”), as depicted in FIG. 2. In these solutions, there is no “cycle” notion, but there may be a boundary on the round robin time, sometimes referred to as “max cycle”. An ONU (e.g. ONU1) reports in step 200, the report is processed in step 202 and the ONU is granted for step 204. Since the reports are processed one by one, the DBA does not have the whole picture of the network load while processing the request.
There is therefore a widely recognized need for, and it would be highly advantageous to have, a DBA method that aids synchronization between the OLT and each ONU to reduce fragmentation loss and increase overall operation efficiency.